Automatic telephone-exchange system



Dec.19,1922. A 1,438,959.

.I. W. LATTIG ET AI.-

AUTOMATIC TELEPHONE EXCHANGE SYSTEIVI.

Dec. 19, 1922.

I. W. .LATTIG ET AL. AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

5 SHEETS-SHEET Z.

ORIGINAL FILED AUG.29, I904.

NQ Nk Dec. 19, 1922. 1,438,959.

J. W. LATTIG ET AL.

AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

ORIGINAL FILED AUG-29| 1904. 5 SHEETS-SHEET 3.

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Dec. 19, l1922.

affimecf/ON 1,438,959. I. W. LATTIG ET AL.

AUTOMATIC TELEPHONE EXCHANGE SYSTEM.

65 6a f fj i Dec. 19, 1922.

AUT-OIVIATIC TELEPHONE EXCHANGE SYSTEM.

ORIGINAL FILED AUG.29, 1904. 5 SHEETS-SHEET 5.

32 Bof/ery I //7 Ven/0h' Jdca VM 0f/7g. f a/@S L Gand/fam.

1,438,959.'` J. w. umm ET AL.

Patented Dec. i9, i922.

nichtsy arasN intatti@ JACOB 'i/VILLLM LATTIG, OF BETHLEHEM,PENNSYLVANIA, AND CHARLES L. GOOD- RUil/X, OF NEW' YORK, N. Y.,ASSIGNORS TO WTESTERN ELECTRC COMPANY, NCORPO- RATED, 0F NETN YORK, N.Y., A CORFORATION 0F NEVJ YORK.

AUTOMATIC TELEPHONE-EXCHANGE SYSTEM.

"o Original application filed August 29, 1904, Serial No 222,657.Divided and this application filed October To f//ZZ whom t may concern.'

Be it known that we, laces lil. Li'r'rio and Crmnnns L. GrooDnUM,citizens or the United States, residing at Bethlehem, in the county otNorthampton and State oi Fennsylvania, and at New York, in the count-yoi New York and State oit New York, respectively, have invented certainnew and useful Improvements in Automatic Telephone-Exchange Systems, ofwhich the t'ollowing is a full, clear, concise, and exact description.

This invention relates to telephone exchange systems employing machineswitching and common battery working, that is to say, a system wherein asingle source oi current at the central oilice is used both tor settingthe switches and for furnishing current to the transmitters for talkingpurposes, and is a division of an application o't Jacob Lattig andCharles L. Goodrum, liled August 29, 1904, Serial No. 222,657.

lOne ot the features ot' this invention is the provision of a circuitarrangement wherein the talking current is fed to the transmitters of apair of interconnected telephone lines over the windings ot a pair otrelays which are maintained energized by such current as long as thetalking circuits, including the transmitters, are closed, and wheneither ot such circuits is opened, as by the replacement of the receiverot' either party to the connection, the consequent deenergization of thecorresponding relay renders operative the restoring means o t theautomatic switching apparatus over which the connection was built up.

Another feature of the invention is the provision of a circuitarrangement for a system ot the character set forth, wherein talkingcurrent is supplied through only two relay windings to the transmitteroit the calling line, and whereby the saine kind of current is alsosupplied through only two relay windings to the transmitter of thecalled line, none of said relays being individual to the called line.More speciti cally, this feature consists in a circuit arrangement formachine switching systems wherein, as the selectors are set in buildingup the connection, the bridging relays used in setting such switches aresucces- Serial No. 196,125.

'Our invention is illustrated. in the accompanying drawings, wherein thesame letters ot' reference point out the same parts throughout. ln thesedrawings,

Fig. l is a diagram ot a subscribers line and substation apparatus,together with the first selector for that line, and its contacts inmultiple banks of various connectors; Fig. l is a diagram of a trunkcircuit leading from a first selector to a second selector oraconnector; Fig. 2 is a diagram of the circuits oit a second selector;Fig. 3 is a diagram of the circuits and connections oi a. connector; andFig. l is a diagram ot a subscribers line, its substation apparatus, andits lirst selector, the connection to the multiple bank o't theconnector oit Fig. 8 heilig shown in heavy lines at the left.

ln reading the following description, it should he noted at the outsetthat the tigures j oin onto each other in sequence, the division lineiineach case being between the wipers and the wiper contacts oi' theswitches. Thus the wipers on the right of Fig. l are supposed to be apart of the same switch and to align with the contacts on the left ofFig. 2, and so on. In order to render the reading easier, the figuresshould be put together as thus indicated.

lite have not illustrated the switch mecha nism in `detail as regardsits mechanical parts, more particularly because our invention is notlimited to a specific switch, but may be practiced with any one of a number of automatic switches. As the circuits are shown, however, for thesake of illustration lwe will1 refer to the following patents, in whichthe so-called Strowger type of switch is shown, this being with somemodifications hereafter referred to, adapted for use with. thesecircuits. The patents are: 591,201, Oct. 5, 1897, AStrowigfer, Lundquistand Erickson; 638,249, Dec. 5, 1890, Keith and Erickson; 672,942, Apr.30, 1901, Keith and Erickson.

l/Ve donot illustrate the apparatus at the subscribers station for thereasons already given. practiced with several types ot appara-tus,although tor the sake of illustration here we have shown the well-knownStrowger type of apparatus. f

Before proceeding to detailed description, we will state theparts andfunctions ot the apparatus which we here show, the circuits for thesame, and the modiications therein caused by the application thereof toour purposes.

ln this system all talking circuits are me-y tallic, that is arecomposed of two line wires; and inaddition we employ a ground return.Each line comes into central and is there connected to its firstselector, corresponding to the answering jack ot a manual multipleswitchboard, and also is connected to multiple contacts in the severalbanks of connectors to which reference will presently be made;

Each selector switch is a sell-contained unit individual to its line,and each contains a multiple contact Yfor each oi the second selectors(in an exchange over 1000) or for each connector (in an exchange under1000). Each second selector is also a self-contained unit, connected toits various multiples in the first selectors either direct or through atrunk line, andeach contains a multiple con* act in its banks for eachconnector. Each connector is a complete switch unit connected to itsmultiples in the various second selector banks (in exchange over 1000)or to the multiples in the rst selector banks (in an exchange underi000), and each connector contains in its banks contacts for thesubscribers lines falling within its range, usually from one-hundreddivision to` another.

j The inode of selection oi' a wanted subscriber, roughly stated, is asfollows: The calling subscriber (in an exchange `over 1000) works hisylirst selector (which is permanently associated with his line) toconnect with an idle second selector in the set containing the thousandsterminals corresponding to Vthe thousands digit in the number wanted;this cuts orf the first selector magnets, whereupon he Works the secondselector switch in a similar manner to the iirst to put himself inconnection with the terminal contact of an idle connector in thehundreds` group corresponding to the hundreds digit in the numberwanted; this cuts ott the second selector magnets, Wherel-Iere also ourinvention maybe upon he works the connector switch to select a multipleterminal of the particular line wanted, As the connection progressesstep by step, the metallic talking circuit is correspondingly extendedthrough the lirst and second selectors and the connector, un-

broken to the latter, but therein separateding subscriber pushes hisbutton and a ringing relay in the connector circuit throws ringing`current on the wanted. line. llVhen the calledv subscriber Aanswers heauto.- inatically works relays in Athe conn ctor circuit which cut backthe main bridged battery on the calling, end oit the talking circuit.lVhen the conversation is finished and the subscribers have hung uptheir receivers, a release magnet in each of the intermediate circuitstrips the mechanism and all of the switches are restored to normal.

Fig'. l shows a pair of line wires 1--2 constituting a subscribers linecircuit and extending' out from the first selector or individual lineswitch@ to several subscribers stations. A', i? and A3. `The station Ais shown in full, connected to the line wires 1 and 2 by the branches 3and l. The stations af, A2 and A3 are all the saine as station il., eachbeing connected across the line by its own pair of branches 5 6, 7 8, or910. The line 1-2 therefore is a party' line, and as will appear laterthe stations are adapted to be signalled selectively. At eachsubscribers station a transmitter T, a receiver E, an induction coil l,a switch hook H, a ringer Q, and condenser C, are provided. ln additionto these any suitable impulse transmitter is mounted on the set,preferably to work with the other apparatus shown, a transmitter olf theStrowger type so arranged asto have successive movements, each; movementtransmittinga digit less in value than 10. lEach transmission sends thedesired number of impulses over the vertical side of line, and

kthen a single impulse over the rotary side incense i inbetore referredto are arranged in horizontal rows of ten or more each (in the presentcase ten). The banks ot rows are bent in semicircular form with thecenter oi' their radii in the axis of the vertical spindle c. In orderto bring the wipers into contact with any particular contacts m and m2therefore the spindle 'v is first stepped up until each wiperis'opposite the desired row, and then is turned around step by stepuntil the wipers come in contact with the desired particular terminalsin the row. The first movement of the spindle is called the verticalmovement, and the second the rotary movement. From these two descriptiveterms the words vertical and rotary have come to be applied to the twoline wires, although in the present system, as will appear later7 theselecting impulses are all sent over the vertical side of line.` Thisvertical side is marked 11 in Fig. 1, 13 in Fig. 2, 15 in Fig. 3 and 17in Fig. 4. The rotary side of line on the other hand is marked 12, 14.16 and 18 in Figs. 1, 2, 3 and il respectively. The terms will beelnployed herein for convenience to designate the two line wires, whilethe various magnets and other parts of the apparatus will be designatedas vertical and rotary to distinguish their functions.

Returning to the subscribers station A, we have said that thetransmitter should send' selective impulses over the verticalk side otline, and a single impulse at the end ot each lgroup over the rotaryside. This is accomplished by transmitting wheels acting in conjunctionwith certain groups of contact springs o. of, o2, a3, at, of, a6, al,as, cr, el, c, am, als, a, and (L15, together with the hook lever' H.The functions of these several springs will appear more particularlyfrom the statement of operation hereafter.

The receiver R is shown in a local circuit 21 terminating in one windingoi the induction coil I, this being in effect the samer as cutting offthe receiver by a condenser so` that battery current will not flowthrough it and its resistance is removed from the line. The transmittercircuit for the common battery system may be traced as follows: Fromvertical line wire 11 by branch 3, wire 25, spring a, wire 26, springa5, spring a, wire 24, springs am and o, line winding of induction coilI, transmitter T by wire 23, and thence by wire 2Q, springs as and afand wire 21 to the rotary side ot line 12, through the branch 4. i

The ringer Q is in a ground tap from branch et on the rotary side ofline, with an interposed condenser C. The spring o4 is grounded at Gthrough a resistance r, for purpose to be presently disclosed. f

lt is to be understood that no substantial change is required in thesubscribers instru-` ment to convert this system back into a localbattery system, the apparatus ren'iaining the same and the only changesbeing in the receiver and transmitter wiring.

Passing` to the central otlice, the metallic talking circuit wires 11and 12 pass through the first selector S, and terminate in the switcharms and f2 of whatwe shall desi gnate as the side-switcli F. Thisside-switch comprises four arms moving together overl a series ofcontacts. there being three contacts tor each arm. These arms are letcred` respectively, f, j, and j. Arm jAl plays over contacts, fo, flo,and 7'20, being normally in contact with f, Similarly and synchronouslythe other arms move over their corresponding contacts during theoperation ot the apparatus7 being normally in contact with the point foin each case.

The` vertical wire 11 is normally connected through arm and wire to thevertical relay D, thence by wire 31 through the cut-ott springs 7c, c2and 7&1 through wire 32 to lthe grounded main battery B. The rotary wire12 is normally connected through arm f2 by wire 3-t to the rotary relayE, thence by wire 33, springs 7a2 and 7c', and wire 32 to the samebattery.

ln their normal condition it is apparent that the wires 11-12 aresevered from the wipers o, and in the severed conductors leading fromthe contacts f2? to the wiper contacts QJ, we interpolate the two equaland opposite windings ot a differential relay shown in the diagram ashaving` an armature o adapted to close upon a contact o, connected bywire 35 with the busy-switch F, through the contacts u and u thereof tothe bridge cut-oit magnet K, and by wire 32 to the main battery. Thearmature o is connected on the other side by wire 36 to the privatecontacts 11132712.12, mit and m16 in the several banks allotted to thevarious parties on the line. We should state that this differentialrelay isused in connection with party lines only. Its winding andconnections are such that under normal conditions ot current flow in themetallic circuit the armature remains unalfectechgand the alternatingcurrentsencounter no substantial retardation,

`either because of twin winding or of a copper jacket. i

rlhe vertical relay D controls through its armature a contact spring CZto close the same on a. ground Contact g. Spring dis connected by wire37 through the springs 722-79 and wire 38 to the vertical magnet D(which actually does the vertical moving ot the spindle e) thence bywire 39 to the main battery wire 32.

iis

The relay E through its armature controls is on this contact the circuitwould be continued through the back release relay J to the privatecontact o2. Normally however this magnet is cut off. f

` The magnet J through its armature j controls the spring contactsjt-and (7'2, which when the armature attracted ground the wire 41 of therelease magnet l, which is connected through wire@ to the main ba'terywire 32. lt will be observed that the arinature of the private magnet Pcontrols the springs p, p2 and p3 the latter two of which also control aground connection for the magnet l by way of wire 3'? and spring (Z. ltis necessary however that both magnets D and l) be energized in order toclose this circuit, and as P is controlled by E, this means that bothvertical and rotary relays D and E must be energized. 4

Although a controlling means is not shown in the drawing the magnet Pcontrols the side-switch F. llllhen the restoring magnet l permits theparts to return to normal, the switch arms of switch F are all returnedto the position shown in Fig. 1. fit each retraction of the armature ofmagnet l). these switch arms are all advanced one step by means of anvescapement controlled by the said armature. This will be referred toagain in the statement of operation.

Before leaving Fig. 1 reference should be made to the magnets L and N,and also to the arrangement of multiples shown. The magnets'L and N areregister magnets, and the multiples shown are arranged for part-y linesignaling. ln considering both of these let us glance first at thegeneral lay-out hereinbefore stated. lt will be remembered that eachline has a first selector such as shown in Fig. 1. This first selectornot only has the individual selective contacts o, corresponding to theanswering jack, but it also has multiple contacts m', etc., with whichthese selecting contacts operate. These multiples fia represent theterminals of wires 13 and 1a leading to the various second selectorswitches. These correspond to trunk lines ina manual exchange, and asthey'are only used at any one time by a limited number of subscribers,they are much fewer in number than the lines of the first selectors, sayamounting toten per cent thereof. The same may be said of theconnectors, which are further extended trunks. Now the multiples m inthe first selectors represent second selectors, and the multiples in thesecond selectors represent the connectors. The multiples in theconnectors however directly represent and are connected to thesubscribers lines and their first selectors. In the drawings Fig. 3shows a connector. The multiple contacts m5 on the connector for theline 19-20 appear in Fig. 4. The same connector' would contain a pair ofmultiple' Vand fm1 belonging to the line 1-2 are distributed so as to belocated in different connectors. 'The connectors are arranged in groups,and since we use the decimalv system in the present case vforconvenience, each group has the multiple terminals of subscribers whosenumbers all have the same hundred digit.` Thus there `will be one groupof connectors for subscribers from 1 to 100, another group for thosefrom 101 to 200, another from those from 201 to 300, and so on. in thesaine way the second selectors are dividedv into groups according to thethousands, and each second selector hasmultiple terminals for all theconnectors within its thousand. rlhus there will be multiples in onegroup of second selectors for all the connectors between 1 and 1000,that is 100', 200, 300, and so on to 900, which within itself selects upto 999. Of course as already stated if the exchange is limited to 1000or less the second selectors can be dispensed with. In each firstselector then levery horizontal row of contacts would represent aseparate hundred, and each contact in that row a separate connector inthat hundred group, all the connectors in one group being duplicates. Toselect a given line the first selector is worked to select-'thethousands or the hundreds group required, and finally the connectoris'worlred to select the line. By preference we put the ringinggenerator connections in the connector` circuit, and since theconnectors are in groups we can give each of several groups differentvarieties of current for ringing, or differently connect the generators.as from; one side of the line to ground or from the other side toground. Referring now to Fig. 1 which shows a party line having fourtelephones, instead of simply multiplying the line to its normal set ofterminals as fmt in the i'irst hundred bank of connectors (assuming itsnumber we will say to be 12), it is multipled to the number 12 terminalsin the first hundred banl: of connectorato the number 12 terminals inthe second hundred bank of connectors, to the number 12 terminals in thethird hundred 4bank of connectors, and to the number 12 terminals in thefourth hundred bank of connectors. The bells at stations A, A', A2 andA3 are all in ground taps from the rotary side of line, each with acondenser, and each adapted to respond to a different frequency ofringing current. A to 2O cycle current, A. to L10 cycles, A2 to 60cycles and A3 to 80 cycles, for ringing. Four generators are provided atthe central oflice, givthe` switch, as inthe iist selectonuntil cut outbythe final. movement of the side switch to its third contacts and thecompletion ot Athe talking circuit fpast the switch.

The `'second selectors are intermediate i n links, in the nature oitrunk lines, and We have reduced-,the mechanism therein to its simplestpossible torni. At the same time itv is to be understood that We mayemploy the second selector circuit instead of the connector circuit :torvarious purposes, such as selectiveA party" line ringing. Thus, insteadof numbering the subscribers on one line so that 'they' fall` indifferent hundreds and hence in difterent connector groups, We mayvnuinberithem so that they ivill lfall iii diterent thousands, `whichbrings them yinto different groups of second selectors. Workingbackthrough the connectors. rihus the ringing be done i 'from the.selectorv circuits if desired.

Referring to Fig. vWe Will describe the connector `apparatus,l and thenWill outline the operation of our entire system, In the first .place itWill be observed that the Wires 15 and 16 Which constitutethe talkingcircuit through the' connector are not electrically continuous, as theyare in the first and ksecond selectors, but are .separated'in the middleby condensers CC.' rlhe 1 urpose4 of this Will presently appear. ltA maygenerally be stated that such sepa-ration enables the control of batterycurrent over one side or the. other, from one station or the other, forsignaling, recording, and the like.

As a matter of convenience, We have designated the ytwo ends of thisconnector circuit as 15-16 and 115"-16, respectively. on- :neoted fromthe Wire 15 by branch 55, isthe vertical relay D4, joined on the otherside by Wire 56 to the spring 57 of a cut-oli relay V.

vThis spring is normally in contact With springs `58and 59, the formerconnected by Wire` 61 with' the spring 6210i the ringing' ture, controlsspring cl3, and the mechanically connectedjbut electrically separatedspring.

d, the latterclosing upon the ground contact g2. The rotary relaylllthr'ough its armature, controls a spring e3, and an electricallyinsulated but mechanically vconnected spring e4k also. adapted `to closeuponv the ground Contact. y Y

ltrvvill be renien'ibered from the previous statements that theconnector not only steps yup its Wiper v5 to the desired row of con*tacts m5but also steps around theWiper to the desired line contact.Hence We have the vertical magnet D5, which does the vertical stepping,controlled by the relay D4, `its circuit passing `from the spring d* by,Way or' thevvire 64C, through the normally closed springs p2, pf of theprivate magnetV the vertical Wire 15 `Works the magnet D5k through` the'relay D4. This places the Wipers vertically."A The single impulse overthe rotary Wire then closes the private niagnet circuit, Asteps the sideswitch F2 Varound one contact with all its arms f, fw, f6", f7. Thissubstitutes for the vertical magnet D5, thei'otarymagnet E5. rlhe finalselective impulses over the Vvertical Wire then Worklthe relay D? andthe' iiiagnet E5 to bring the' Wiper @5 on the contacts m5 of the linewb2@ Wanted. rlhis series otimpulses is olloWedby a `single impulseasbeore, over theA rotary side of line, Which again actuates theprivateinagnet and this moves lthe side switch lT2 into its third position `sothat its four arnis rest upon their last contacts jm.' The arms fm1 and7"0, it Willbe observed, have completed the talking circuit (marked inheavy lines),

and the rotary and vertical magnets are en- The ringing relay l/V, how

tirely cut out. everis cut in by Way of 69 and ,corr tact )"20 throughWire 65 back to the contacts of relayy D4. lVhen the callingsubscriberhas gone thus far, he presses his ringing button, and thereby grounds`the vertical side of `line once more. This energizes the relay D4,completing a circuit from ground through springs g2 and d, Wire 64,springs l@tandA p, Wire 65, side-switch arm fio sideswitch contact f2",Wire 69, and relay W to battery. This ene'rgizes the ringing relayv lV,which breaks the through talking circuit and connectsthe ringinggenerator Wire 175 through the spring f'lto the rotary ivire 16 on thecalled side of the break, and so tothe Wire 18, the ringer Q and ground.

` The two magnets V and V. are bridged across the line, ivith the mainbattery `interT posed.k They both receivecurrent when the calledsubscriber answers, this flowing over the metallic circuit 15-17,jl9-station i4-l 20-l8f`16, and back to batter'.

on :relay a7', isadapted to comple across the calling end oi"tlie`line,"iiicluding the battery Band the relays X and Y, by thefollowing path: lbattery B, Wire 71, magnet Y, Wire 72, spring 73,spring 74, Wire 75. Wire 16, back to the calling subscribers stationthrough the Wires 14 and, 12, out again through the Wires. 11 and 13 to`the Wire 15, and by Wirev 7 6 to spring "7, spring 7,8, Wire 79,' magnetX, and groundpback to the battery.` TWhen the magnet Vf is energized,this lli) lll?) tial registering, several batteries may be em-r ployed.

The trunk circuit shown in Fig. 1a will now `be described with specialreferenceto the automatic system herein shown, ybut it will beunderstood'that its use is not limited to this specific system and thatit is applicable to any system of signalingin which repeating isrequired.

. In Figure 1f"^,`which is supposed' to be interpolated betweenfFigure 1and Figure 2,

we have shown the multiple contacts m in the banks oi theiirstselectors, connected by the trunk wires 13-'14 and 14-13 to asecondselector. which may oryinay not be in the saine exchange as theirst. ,Each side e oi the trunk is,conductively.divided `but inductivelyinade continuous by the condensers l2 The. wire 13e-14 continues asthe,` vertical side offline, while the wire 14--13` continues the rotaryside;

e cannot pass the condenser C2 directly, but

inust` be repeated, and the same with the other sideot line.y Wetherefore provide thel repeater Z, having its magnet .e con nected tothe wire 14 by the wire 90, and. thenceby wire 91 through' cut-oilcontacts. 92, 93 and 94 to the'lbattery B3. Similarly'` the magnet a isconnected by wire 95 to wireI 13 and thence by wire 96, throughcontacts'. 93 and 94 to the battery B?. 92, 93 ,andr 94 are normallyclosed, but adapt ed tobe opened by magnet Z5, which is .in-

a branch circuit 97-98 extending from the battery T3 vto two magnets Zv.and Zzby branches 99 and 100, and thence to the respective contacts 101and 102 oi the oppositely polarized relays Z3 and Z4. These `re-` laysare in series inthe circuit 4103which terminates in the twocvontacts 104and `105y lying on'opposite sides ot' the ground' con-- tact Y10S. `Thearmature z2 of the. magnet controls the long spring 106, `and the arma-lture of the magnet 1 controls the-long spring 107, and these twoarmatures. also control the -springs`104 and 105. When eithermagnetl isenergized, itr grounds its. spring 104 or 105, and when both areenersriaedtogether they close' the contacts 106y and107 together. l i

' The magnets Z- `and Z2 respectively con-.

trol the armatures 199`and 110, which in. turn control .the continuityof' the branch..

'i circuitslll and 112 with the back supply' circuit` 113,. `Each oi?these branches `has a,

. battery connection, and thesebattei'y con nections, are relativelyreversed, asshownl `by the batteries Bf and B2." Adapted to bei "bridgedacrossfthefcircuit 13-14 with one. y ,or the `other orp the batteries Bor v B?, through thecircuitll and the ground re-,vH turn 114, ,are thetwo' magnets vZaiid Zh@ eontrolling the first a `iront contact llyiand.V

.the second a back ycontact 11G. VVheI-i'both.-

e impulses comingy over the vvertical side tor'the second ,selectorvwhich the repetition goes'.

The contactsk v.magnets are attracted, one contact is open,

and the armatures are connected in series at 117`4 These armatures andthese .contacts Y- gointly control the continuity of the branch 118 ofthe trunkrelease circuit- 119 leading from the battery B3 to the backrelease contacts m2. e e. parallel branch 120 is con-` trolled by thetwo springs 10G-107.

impulses over the lwire 13 aect the inag-` Iiet.e which repeats intothewire 13 by grounding its contact 105, and thereby` grounding` the saidwire 13" through the branch 123.

Similarly, impulsesv over the i wire 14 aiiect the magnet which repeatsi into the wire 14 by' grounding its Contact 104 and thereby completingthe branch 121. Or-

positions, but these are not necessary always,v

.and in fact, when wespeak oi a transposition at125, the term'ismerelyrelative, as

we mean by this only the connection of the wires `121jand 123 `forrepeating, to opposite sides troni those inductively `through thecondensers to the sides infV the respective impulses originate. v Inthis Figure-1a therefore, there are shown two principal features ofinvention, both of which, togetherwith others, we shall claim broadly.The` first isv the transposition for lrapid repeating forwardly, and thesecond is fthe control of the batteries B and B2 so that "when currentof one direction or the other iis cut back over the'metallie talkingcircuit Afrom `the connector cut `on rela f- V" or in :any other way,the repeated current sent back will be automatically controlled throughthe trunk as to its polarity. This is important in the registering, paystation, and other work which lwehave mentioned as requiring `polaritycontrol.

The operation of our system, apparatus `:and methods will have beenlargely under- ;stood from the preceding description; but lwe will herebriefly review the saine.

` Taking the system shown in Figures 1, 2, 58 and 4, we will firstassume a call originating overthe line lf2 from the station Ay (numk ber1,2) andintended for station A4 in lFigure 4.' Subscriber A firsttakesdown his refseiver, .R and turns his impulse ltransmitter (notshown) sothat after the rising of the "hook a ground circuit willbe'completed from connected which ineens@ G through the resistance frand contacts LL-0J to the vertical side offline l, current flowing outover this path `iroin the battery B through wire S2-,contacts 1li', Ig?,7c3, Wire 31, relay D and linefivire il; The iirst nuinber of iinpulsessent we will say is one, assuming the nun'iber ofstation t? to be 1920.`

Relay D controls magnet l to `step up the spindle '1i until the Wiper eregisters With `contact Vm in the first row of second selector contactsin the bank. its theiinpulse transniittei' at station A coines tore-st,it inoinentarily closesl together the contacts if-a?, which sends oneimpulse out from battery B through wire 32, springs /-f c2, Wire 33 andmagnet E over Wire 34, side switch Wiper f2 to wire 12 to thesiiibstation and to ground. Altlagnet E attracts its arinature andcloses spring e on the ground contact g, thus coinpletingy circuitthrouejh the private magnet l?, which opens the circuit fil-38 oi? thevertical magnet, and l vertical stops any turnier inoveinent ot thespindle. lt also lets the 'side switch F step around `one contact. In

doing' so, the arni fo passes onto contact `flo and so cuts inthe magnetE', which iniine diately takes current through the Wire 39, and batteryWire 32, vibratingr continuously until out out. Thisyibration isproduced tracted, this being represented in the diag-rain throughout bya pair ot points normally touching each other between the niagnet coilsand adapted to be separated by an insulating; point on the arn'iature.The'ariiiature also rotates the spindle 'a sov that the Wiper o passestroin one pair ot multiple contacts to another, touching one before itleaves the last one, and continuing reaches an idle pair, which means anidle second selector, which again iueans a selector without any groundon the Wire 4:9. By making the Wiper bridge the contacts Without a breakbetween thenv i passes over those that are busy because the busy ones,being grounded through the Wire e9, hold' up the iiiagiiet l) by currentover the following path: liattei'y li, 32, l), 390, 4&0, flo, f3, J, 52,o2, m2, a9, and ground. Theinstant an idle selector contact is 'reaihedthis grounded circuit is broken, and the magnet P lets go its armature,with the result that the side switch .by the armature separatinercontacts when at- F is released for 4the second step, the rotary inagnetE is cut ci? and the aria jj' is open, the arnis 7 and ,t2 cach passonto its tliii'd contact im, conipleting the talking circuit anddisconnecting the rontrolling relays and magnets therefrom, `while theainr ji? passes on to its third contact and closes the ground by Wire 5eto the wire V" through magnet J 0i) and Wire 52 to the Contact wiper v2,contact fm? and wire e9, this being utilized later on in restoring` theapparatus, as Will be noted hereafter. i

Vile new have the station fr einueoted through to the second selectorcircuita ,'llhe callingsubscriber again turns his transmitter plate tosend `nine impulses, by closing the contacts ffr-fr? together nine timesand afterwards the contactsv (Lf-a2 together once `as before. The nineimpulses cause 'the vertical relay DE to be energized nine times over acircuit troni battery, Wire 32, through the magnet D2, Wire Ll5 and Wire13, back through lwire llto the substation. Tlieiinag net D2 attractsits armature nine tinies to Aground the spring (Z2, thereby closing thecircloses circuit liroin battery. Wire 32, tirough the private magnetP2, the latter opening the yei'tical magnet circuit D3, and permittingthe side switch F to nuove all its arins fff,

n J i Y i i j and around one step, the arin fT ciitting in the rotary.'magnet E3, and the arm t? connecting` the wiper @t bach through` themagnet vl and P2 to the battery Wire 32..

The rotary magnet, being,` in circuit, coniinences lto vibrate and steparound the spindle @as before, until the `Winer e3 and` Wiper` if* iindcontacts of connectors are idle,

or, inother Words, ungrouiided. fnlf this `connection we should callattention tothe 'tact that the ins-ant the spindle n in Fig. (firstselector commenced to rise, it released a springe' (see the lett-handside of the iniguie) of a switch breaking circuit with contact if/ ofthe bridging cut-ofi relay K. around until it and reundinn1 the Wire onthe contact er. This completed a circuit troni ground as tollows: Si,u2, u, S5, 0', o, 3G, and to ,all the contacts m10, m12, m14, and m16 inthe` iniiltiple banks oit connectors upon which connec tion ntie-lit beiiiade" with `the line il-2.

private bank contacts grounded..k uf'ill test busy, thereforew it anyoneelse attempts to break in by calling' line 1 2 or any of its stations.Similarly, the instant connection Wasinade between the first selector'and the second selector at c2, fm2, the side switch arin f3 incre/l iitoits third position, connectin- .ground to the Wire till, and so throughWire 53, magnet d, and

Wire 52 to the Wiper n2, and thence4 to all the connected multiplecontactsm2 of tliesecond selector shown, where-rer they might bedistributed1 so that no first selector could 1et in en that secondselector 'While thus in use.

es soon as the second selector finds a con-y nector that is idle, theground circuit through magnet P2 (Fig. 2) is broken, the side switch li"makes its last step, the arms and j complete the metallic circuit lf3-14onto lli-16, the arni f* cutsk o'the rotary all being i iio iso

niagnet, and thereafterremains open, and

' the arm '7 closes the Ground of contact '2 onto themagnetwd, and so tothe wiper 04, which, being on the Contact m4, makes it and its connectedmultiple' contacts ot the connector thus selected test busy thereafterduring the connection.

that it controls the circuits of three magnets,

the` vertical magnet' D5, therotary magnet E5, and the ringing relaylll.. I

The suhscribernow sends the number 2, which causes two impulses to passalong the wires 15, 13, 11 and 1 and toyground at station A, through theconnector circuit as-t'ollows: latteryl to spring 59, to springs `58.and 5 7, wire 56, relay D4 and wire 55 to wire f 15. This vertical relayi t is thus energized andgit in turn closes a circuit. containing ymagnet D5 which then stepsup the spindle e until its wipers o5 and oreach their `respective second rows of subscribers contacts.

The single impulse over the rotary side 16 kof the line fronithe batteryB `by wire 32, vsprings 59-k-58`, wire 61, springs {i2-63, wire- 6 0, torelay E4, wire 16, and back rto the sube scribers station operatesmagnet E4 which grounds the spring et, closing the? circuit of theprivate relay P3." ln moving its armature, the magnet l?? lets the sideswitch goi around `one contact, cutting in 4the rotary magnet E5, andconnecting the wiper o6 thrbugh the arm'fmand contact f1, to the s rino'3 to re area circuitto releasethe` connector it the desired line istound'to be busy. The subscriber now sends the nuinbe-r O, which is tenimpulses over' the vertical side of the line. This again works thevertical relay D4 as before, which grounds the springe?4L and this timecloses the circuite,

Y 6,5, G8,l 6'?, 32,13, of the rota-ry.magnetI E5.

This brings the 'wipers o5 yand 'ef'onto the in-` dividual contacts 'm5`and m6 in the multiple bank of the connector if in Fig. L The consequentgrounding of the rotary side of the line at the substation will operaterelay E4. The operation of relay lllt will close the circuit containingymagnet P3 and the operation i offtlieflatter4 will close-a contact atsprings gi' and ya, `Now, itt the called line is busy, the contact mwillbe connected to ground,

'l as a result either of the operation of switch U (Figli), or, due tothe ground circuit, to wiper o by way of side switch arm f7 of theswitch used in the set-up connection. There f tore, when the magnet P3is operated and the wiper o? is lconnected to busy line,` a circuitwillbelcompleted from ground'by way of wiper v6," arm f7?, springs p3and p4, yrelay J2,"

allec-t the'side switchF2, and asthe connec-` tor switch is released assoon as thel magnet P2 is operated `When the called line is'busy, theside switclrl `2 vis likewise `released and cannot pass out ol itsnormal yposition when the magnet P3 is deenergized.

The calling subscriber will next operate `his ringing button. This willclose a 'circuit containing the verticaly relay D4 over a path togro-und, from the subscriliies station (Fig. 1), through resistance r,contacts 0f, c2,

al?, a, a2 and z5 tofwi're 25, vand thence by.

wires 3, 11, 13 and l5 to the vertical relay E4, wire 56, springs 57,and 59, wire 32 to battery. The operation or" the vertical lrelay D4'will close the circuit of the vertical mat,- net D5, which'in turn willraise the spindle e one step. As soonv as thefswitch takes its firstVertical step Vtroni normal, springs 101 y and102 oi theoil-nornialswitch close and thereby complete a` circuity `fromground to thesecondary busy-back ltransformer, springs 101 and`102 and sideswitcharin `fotothe rotary sidel of theline, vand thence out to thesubstation and baclr on the vertical'side oi' the line and through relayD4', to battery. This gives the calling subscriber the busy tone. Thecalling subscriber will then hang up hisreceiver and will therefore.momentarily ground both sides oi' the line which will simultaneouslyoperate relays D* and E4. Thesey close their Contact springs athes' atpoint whereby the following circuit is completed: Battery l3,wire 32,d'2, c2., (Z3 to contacts m4, wiper et, magnet J arni y", contact f2 andground. The magnets J. and J 2 bothv act, thelatter to restore thevconnector S2 and 'they ornierto close the circuit B, 32,

50, I', 51, 49, m2,'o2,52,` J, 53;, arm' f2, contact f2, 5ft, andground. magnet 'l'l pulls out the pawls that hold the spindle/v oit-thesecond selector S (F 2), and restores this to aero; while the rela-y Jclosesthe circuit of the release magnet l as ollowszBattery B, 82, 4:2,l, l11, j2, 5;",and to ground. whereupon magnet l pulls out the pawlsfrom the spindle U of the first selector (Fig. 1 ),5, and permits thatto go to Zero. The magnet l, magnet l and magnet J2 in each case, whenreleasing the pawls from the vertical spindle also pulls over the sideswitch E, E 'or E2 to the normal or :cero position shown in `thefigures. When the spindle@ :oie the first selector S drops. down,

littakes the ground off the wire 35 by pushing down the spring u of theswitch U.

Thus all parts are again normal andA ally iso switches idle.

lil/Thereupon the rasante Suppose. however, that the line Wanted doesnot test busy. The subscriber, after sending in his last number presseshis ringing button which closes a contact at the springs cl3 and alt toground the vertical side ciLl line as follows: G7 r. springs etwa, (L13,am. o6, 1,5 and by Wire 25 to the vertical side oi*l line. This permitscurrent to pass back from battery, Wire 32 in Figure' 3., throughvertical relay Dt to the subf-ecribers station and ground. The spring d*is airain grounded. and a circuit is Completed troni ground, throughsprings 7a2 79 and Wire G5 to arm f4". contact feo, Wire G9, theringingv relay W and battery. llhis relay attracts its armature andthrows down the springrs tl'iereoil".y opening` the vertical side otline l5 entirely. lt also opens the rotary side of line lo and connectsthe iforivard end thereof throuoh its terminal Tl to the ringrinu'generator vire 170. Current thc 1 casses ont through Wire i6. lowercontact re i8. Wire Q0, ringer and to ground through the condenser atthe Wanted sta tion A4.

jitter ringing., the calling` subscriber i releases his callingbutton,the vertical rclay and the ringing relay in Figure Slet so? and themetallic talking;v circuit is clear through from one station to theother7 as marked inheavy lines, except for the `interposed condensers f.all magnets and re- I Ll n lays are disconnected, and all urounds areoil?, except that the inaenets D1' and llt are connected i'roin the ve:al and rotary slo of the line. respectively. to the springs of thecut-oii' relay V. and these sfarino's in turn are connected to thebattery lt; nl reas the magnets V and V are connected in series with thebattery l? this circuit beine; bridged across the Wires l-l6 leading; tothe called subscriberlsI station n.4. The latter bridged connection isyadapted to give current to the subscriber A? in llcjure l overhisvnietallic circuit; but .it should be particuh rly. noted that there.is no bridged talking' battery on the metallic circuit back to thecalling' subscriber.

The called subscriber A4" We will suppose now answers by tal/zincT downhis receiver. His sritchhoolr thereupon rises and closes his metallictalking circuit. whereupon current tlorrs troni the bridged batterythrough the tW magnets V-V out to the station A4 and back. Both magnetsattract their arnuttures.J but the springs of relay V breal; contactbefore the springs of relay V maire contact, and thereby cut oitlthevertical and rotary relays Dt' and before the magnets X and Y are cuton. with their bridged battery connections. lit it were not for thiscutfoil there would be a short-circuit through the relays Dt-lk whichwere bridged. and they Wouldwork the release :aan

mechanism by closing their contacts d3-c3 at the point aff.

y lfihen the inagrnet lf acts, it cuts on trie relays and Y Vand bridgestie niain battery across the connector wires .l5-lt, `so that talking'current non' flows back through the metallic circuit to the callingstation A. tiubscriber A thus rests current for his tel' phonetrai'ismitter T.

Both magnets l anc tlT non: hold vup their armatures c the connection,and it is to be observed that this keeps the release circuitsrot thebaciv release relays open, bec the contacts 5c ot the magnet X- op jaltliough the others e/-jz/I" are closed. The D4 and lll' being cut out,their release contacts are open at ai.

t t ie conclusion of the. conversation, when subscriber hang' up,j hebreaks the metallic circuit and i `nientarily grounds liioth sidesthereof by closingh together the springs al. au. cl2. 'the ogeninc; or"the subscriberis loop deenergizes the relays X and Y. d the subsequentmomentary grounding or both les of "the line momentarily enerrjizcsrelay Y, as previously eX- il ned. lllhis closes a circuit from the ndon side switch Contact i320, by way of side switch arm *'7 and relay Jto Wiper Contact et and` contact mt, and thence by Yway ci wire thcontacts a?? and ai', wire 70, contact y and y to release magnet J2, andbyway otl Wires 750 and 32 to battery. The release magnet J2 will thusbe ener- `gr/Jed, and in drawing up its armature it pulls out theretainini;` gan'l ot' the spindle o ot the connector. Fig. restoring;'this switch to normal. The relay JQ 2, closes the local circuit oit'the release magrnet l. ot the second selector through `wire 49. and theback release relay l oi the tiret selector, which in turn closes thelocal re-v lease circuit ot' release magnet l ot the vfirst selector.The operation oi the release mau'- nets associated with the variousswitches Will restore all or" these switches to normal. lt the subs thangs un his receiver and V Will be deener- The magnet V `will be momenyreen/cruised however9 1when both sides the are momentarily grounded. therelease circuit through iereinbeiiore described7 and tches will berestored to norr similar to thatdescribed vscriher'r the first to hans'o it This will close ribed the operation of system tor a complete backUhe talking.;- battery to the ubscuberwhen the called subscriber on therelays and n'iaejnets Ot toll boues or u 2 y n' l t remains to describethe opergroup` ci second selectors in the saine or ditierent exchange.ln Figure 2 will be found a line marked lineot trunk connection. Theends ot the tufo wires 13 and 1/1' in Figure l.a are supposed to beconnected directly to the Wires 153-14, where they are cut by this line,the Wire 49 in Figure 2 being the same as Wire 49' in ViiigureConsidering the trunk line to be interpolated between the first andsecond selectors therefore, and `having the trunk broken by thecondensers C2, the operation is as follows: Y

rl'he transmission ott impulses and selection of an idle trunkthrough'its contacts m' m2, is Vthe same as before, the iirst selectorthen connecting` the subscribers line through on tothe trunk, just asheretofore We have described it as connecting onto the the secondselectorcircuit direct. The second set of impulses coming along over thevertical Wire 13 cannot pass on into the second selector circuit directbecause vof the condenser. Their lcircuit is from the batteryB, throughthe springs 94, 93, and

by Wire 9G to magnet Z', Wire 95 to Wire 1o, and so bach to thesubscribers station and ground. ,The Imagnet e' when energiaed groundsthe contact 105 by forcing it against the contactl 108, and therebygrounds the wire 13 by the following path: 13', 124, 123, 105, 108, toground. For each impulse, current ivill then flow baclr from the batteryB, Figure 2 through the vertical rela-y D2, through Wire e5, Wire 13,Wire 13',

(Figure 1a), and so to ground as stated. The operation of the mechanismin the second selector circuit is the same as already described.

VThe single impulse that comes'over the rotary side 11i travels throughthe circuit lli", 911, 93, 92, 91, a, 90, 111, and back to the callingsubscribers station. grounds the contact 104i at 10S, grounding the wire14;' through Wire 121.

1t Will be observed that each impulsethat comes over the Wire one Way orthe other means the charging of the line and the charging of thecondensers, with a subse quent discharge. .iccording` to ourarrangement, however, an impulse over Wire 13 would affect magnet a' andrepeat into the Wire 13', While `the condenser C2 discharges across intothe wire 14C', Which is not re 4is into the Wire l The magnet adischarge `trom the condenser of Wire '14- The transmission vof allsubsequent impulses to the selectors and connector is the same. Thisbrings us to the next step, which is the cutting back of battery of theproper polarity When the called subscriber answers. j It Will beremembered that the direction or" current flow which Toes back to thecalling subscribers station is determined by the direction in which thebattery B is connected across the circuit 15-16 by the cut-on relay V'in Figure Flow of current from this battery cannot go all the Way backto the calling subscribers station, however, becausey oi" thecondensers, not to mention the drop that would result` from theresistance of a long trunlr it there were no condensers. We will supposethe connection to have been completed, and the called subscriber to haveanswered. His answering energizes the relays V', V, which cut on the`battery B across u'ires 15-16 and send current back through the wires13-1f1, and from the latter through 11i', 121, 104, contact 130, bridgeWire 103, through the two polarized relays Z3 and Z4 in series, back tocontact 131, spring 105, Wire 123, and Wire 13 to the Wire 13 and backto battery.

The direction in which the battery B is connected across the circuit inFigure 3 determines which of the relays ZS-Z4 Will attract its armature,for these are oppositely polarized. .Supposing it to be Z3, this closesthe local circuit 101, 99, Z',s93, Z5, 97, battery B3, and ground.Magnet Z5 opens the circuit of the repeater magnets e and e' at thesprinos 92-93-94, this being necessary to avoid the attraction of theirarmatures With consequent interference. At the same time the magnetl Z'closes the circuit 114, B', 111, 109, 113, 7 6, Wire 14e, back -to theCallingsubscribers station, out again, Wire 13, magnet Z7, Wire 114i',and ground back to the battery B. ln other Words, batter B is bridgedacross the Wires 13-14lvin the same direction as the original batteryinthe connector circuit, Figure 3. Suppose that battery to have beenreversed, then the polarized relay Z4 would have attracted its armatureand connected thereversed battery B2 to send back current. Thus, thedirection of the current supplied to the calling subscriberA iscontrolled through the repeaten It the trunk line is very long, severalof theserrepeater .circuits may be. used to oil-set the excessive Thisbrings us to the question of releasing, which is the last step to beconsidered. The

magnets .e and e' on the calling end of the iso resserre trunlr whenthey both attract their armatures close the contacts 106 and 107together, thereby closing the branch 120 of the release circuit tracedas follows: battery B3, Wire 119, 120, 107, 10G, 120, 119 and contact m2in the multiple bank m of the iirst selector,

Figure 1. thence in Figure 1 by the Wire 52 y through magnet J and toground. Relay .l Works the release magnet l to return the iii-stselector to Zero. The simultaneous attrac- J'ion of the armature of reljs s and 2 will likewise simultaneously ground the two sides 13 and 14of the trunlrcircuit by ineens of their springs 10i and 105. ylhis willcause tlie restoration to normal of all of the rest of the switches usedin setting up the connection. This is the release that would occur ifthe subscriber A hung up Without completing;` the connection. After theculled subscriber has answered, however, one of the batteries B or l) An2 is cut baclr and bridged across the calling end 13 111, and at thesaine time the magnet Z5 opens the contact at springs 02-93-0%l and cutsoff the two magnets and e. The bridge through these internets is openedto prevent their opH eration by the bridged battery and a consequentpremature release of the switches. Home means must therefore be providedJfor breaking` the connection and .restoring the first selector in casesubscriber A hangs up lirst. 0f course, if the called subscriber hangsup first the magnets e and e would airain be cut in and then, When thecalling; subscriber hung up, they would act as we have stated to clearout. The magnets Z and Z7 serve to control the releasek of the firstselector switch from the calling subscribc1s end when thecalledrsubscriber has his rece'rer off the hook.` llVhen the callingsubscriber hangs up his receiver before thc called subscriber does., heopens at the sul rrril'iefs station the circuit containing: the magnetsZ" and Z7, which will therefore be dcenergejized. However, thesubsequent ino ineii'tary rounding); of both sides of the line willrecnei face magnet ZG. This closes 'the release circuit. from ground.(Figql), wire 531i, f e switch contact f2", side switch arm f and relayrl to wiper o2 and contact 'm2 (Fig. l0). wire 110 contact 115 andarmature of relay Z, armature and contact of relay lill, Wires 118 and119 to battery B3. Thus relay yl will. be energized. relay l will causethe operation of release magnet .l which will restore the first selectorswitch. i

l/Ve shall new briefly sta-te the operation Where a subscriber on oneline calls another subscriber who is on a party line. The first stepsthrough the first selector to the second selector are the same as theplain connection We have heretofore followed. Then a divergence. Vilewill assume there are .four parties on the line, as shown in l, 1t

the same hundred.

`for party line ser, `is a unit 'ior calluii';` in, hariugi but one iiiiaiiaaie The actuation of Will be remembered thatl all the connectorssuchas shown in Fig. are divided into groups, each grouphaving'inultipled to its respectrebanlrs fm, the subscribers Wires1'7-18 whose numbers are comprisedwithin Thus there Would be one groupof connectors in which there are contacts for subscribers from 1 to 100,another greup for subscribers from 101 to 200` anotheifroin 201 to 300,another from 301,75 to 400, and so on. The second selectors aresimilarlydivided into groups with regard to the thousands. ln otherWords, there would be one group of second selectors containing contactsof all the connectors from 100 to 900, another group for those from 1000to 1900,l and so on.. As heretofore traced, in order to select suoli anumber as for instance 1920, the calling subscriber Would puthiinselfonto an idle second selector in the second 'thousands group, thenthrough that onto :in idle connector in the ninth hundred group thereof,then through that onto its :nui '90 line contact. New ice, of course.each li c 'st selector switch, or in a. manual exchange one answeringrjack. But for the purpose of beingr called,we regard each subscriber onthe party` line as a separate unit, and gire hiin a. separate lineterminal, corresponding to a multiple jack. The four `.subscribers onthe one line have their four calling` terminals (or multiple jacks) infour different con' nector groups, which is the same as to say that eachsubscriber has a different hundreds number from the others.v New, in thepresent case We hare assumed` the foursubscribers A, A', A2 and A3 to benumbered and 312, respect' ly. The niul- 105 tiple or calling terminalsofsuiiscriber it are therefore found only iu the `first l'iundred bankor group o' connectors, as indicated in lith-mm in Fig. l.`blul'isiiriber ill has his multiple connectingq terminals in thesecoiul ..110 hundred group at inn-.f l" luhscriber if has his multipleconnecting terminals in the third hundred iup at wiltwvnlm. Andsubscriber A3 has hisA terminals in 'the fourth hundred group atveli-712,1, But, it vvwill be remembered that the ringing' generator orgenerators are connected in ythe connector groups. We can therefore gire'a different kind of ringing current, or a difl'erent path for ringinglcurrent to each separate hundreds group. Thus to the connectors in thefirst hundred group we preferalily Igive a generator furnishing say 20cycle alternating current;` to those in these/cond hundreds group agenerator giving current at cycles; to the third. hundreds group 60cycle currentgand to the 'fourth hundreds group yio line -Q, and as Alsringer only, on'that line, is adjusted to respond to that particularcurrent, his bell will sound to theeclusion` of others.

Similarly, in calling rig, the calling subscriber would go through thethird group of connectors,y because, i- 2s number is 212. This group ofconnectors has cycle current only. Hence, thebell at stat-ion :l2 onlywill ring. i

W e have described the use of ringing current of different frequencies,but We Wish it clearly understood that We are not limited to this. illevmay use any of vthe devices lrnoivn in the art for selective ringing.For example, the bell at station. A may be polarized for plus'current,and be Wired in iii ground tap from No. 2 side of line. Bell atstationifi may ybe polarizer for minus current, and be Wired in a ground tapfrom the saine side of line. Bell at station il? may be polarized forplus current, and the bell at station A3 for minus current, and thesemaybe Wired in ground taps from the No. 'l side of the line. To selectone or they other station the connectors of the different groups wouldbe larranged to place positive or negative pulsating current to one sideor the otherof the line desired, according to the group. Step-by-stcpselectors may also be used, by providing each group of connectors with anialre-and-break device sending a distinctive number of impulses. i So'much for vthe connection of a party on one line through another line toone of several subscribers thereon. More diiiicult vis the problemr ofhoiv to permit a subseriber to select and call another onfhis own line;As We have shown, the moment a lirst selector switch starts it puts aground on the private line or busy terminals 1n/1". r

energized,'vvhereas, for current in one of the line only, the magnetWill lift its armature o olf the contact o, and thus disl connect theground at switch U from the private line contacts m10, m12, etc. Thisprivate banlrl circuit is` normally as follows:

p impossible in practice.`

`Ground. u2 fu, 35,0 3G and to the irivate bank contacts. rl'he contacts0 0', are closed at all times except pist at the instant vthat impulsesare being sent over one side some one else might get in, but this isalmost Suppose noivthat ealls iii.r He starts the first selector S, thesecond selector S and the connector' S2 in the second hundreds grouprlhe connector steps up its Wiper o5 to the second rou7 of contacts m11,then steps around one to the second contact in the row. The impulse thatproduces this step is going'through the rertical side of the line, ll,and raisesthe armature 0 for the briefest fractiony of a second, just asthe Wiper o5 comes on the proper Contact. lft stops there, and the busytest circuit is closed again.v lis amatter of fact the armature o, if`made properly, Will respond to each impulse, an'd'therefore thebusyrcircuit is never open kat oner time for longer than'perhalsone-tenth or less of a second.

vThus, the subscriber comes in on his own line. As yet there is no floivof current in his metallic circuit for talking, this being controlled bythe called subscriber back through the connector' relay V. The group ofconnectors'he has selected automatically give Ll0 cycle current, andring the bell at station i. 1When A. answers by taking down hisreceiver, talking current is cut back over the calling end.

F or a party line system, in Awhich the subscribers ringers are bridgedfrom either side ofthe line to ground, special provisions must be madefor the actuation of the ringers tapped from; the vertical side of theline. The resistance rat the subscribcrs sta-tion is used for thispurpose. lt will bo evi-A dent, if there were no resistance in thecircuit to ground, that the subscriber, upon depressing his ringingbutton, would put a short circuitv to ground on` the vertical side ofthe line. "This shunt would rob the ringers of the necessary currentrequired for theiroperation. The resistance r is therefore made highenough to prevent the shunting of the major por ion of the ringingIycurrent whichV Will therefore seek a kpath through the desiredsubscribers ringer.

The resistance 7 at thesubscribers station i is further useful inpreventing a premature disconnect on a party line connection. Thus, thisresistance r prevents a premature release by a subscriber on a partyline, vwho cuts in on a connection which had been previously establishedwith anothery subscriber'on the'same party line or some other line. 'ItWill be evident that'if a connection vvith a party line subscriber hadbeen established, that asecond party on the party line,

and

i ,assess upon cutting inon the connectionand hauging up his receiver,would momentarily ground both sides of the line.` Therefore, if theresistance i were not included in the ground tap at the subscribersstation, both sides of the line` would obtain a momentary connectiondirect to ground. rThis direct ground tap, to the vertical side oli'.the line wouldfshunt out the relay X at the connector circuit, and thedeenergization o' relay would close the release circuit and restore theswitches 'to normal, as previously described. However, when the groundtap at the subscriber is wired through the resistance r, the relay X isconnected to ground ing parallel with the resistance fr, and in thisinstance suiiicient `current will flow through the relay X to maintainit in its operative position, 'and` thereby prevent the prematuredisconnect;

Although we` huye specified a line between the iirst and` secondselectors as the line for trunk connection, we have shown another placein Figure 3, marked trunk connection, where extended trunks such asshown in Figure la may be inserted. Similarly, they may of `course beinserted at a corresponding point in1 the first selector circuit ofFigure Ll. Our invention is not limited to any particular location ofthe trunks.

`We are fully aware that many changes may be made in matters of detail,and even in some broad features oi' the system and apparatus describedherein, without sacriicing or departing from some 0r all ci the featuresand vprinciples ot our invention. Thus, the central-energy currentsupply system m'ay be divorced from the' party line scheme. By simplyomitting the common battery features,` particularly in the connectorcircuit, and supplying` local batteries at the subscribers stations fortalking, the party line features may be used with perfeet success in anyexisting. Strowger automatic system. Similarly, the central' batteryscheme can `obviously be used i with other circuits, and without partylines. lt must be understood that all such changes lie entirely withinthe scope and purview of our invention.

That is claimed is:

1. ln a telephone system,` automatic switching apparatus normally atrest for extending a connection fromi a calling to a called line, meanswhereby talking current is supplied through only two relay windings tothe substation of the calling subscriber, and whereby the same kind ofcurrent' is also suppliedthrough only two relay windings to thesubstation of the called subscriber, noneot said relays being individualto the called subscriber.

2. A telephone system comprising a line circuit, a transmitter in saidcircuit, a source 3, A telephone system comprising` a line r circuit, atransmitter in said circuit, a source of talking current, a condenser ineach side of said circuit.l bridging relays distributed along saidcircuit,y switching means controlled by said relays, means for cuttingolil all except a pair of relay windings on each side of saidcondensers, and means lor supplying current only through the remainingJfour windings to said circuit for talking purposes.

Ll. A telephone system including a calling` l l and a calledsuoscriber's line provided with `terminal contacts, ,an automaticconnector switch, automatic means for connectingthe terminal contacts otthek calling line to said connector switch, subscriber controlled meansiior then operating said automatic connector switch to extend the callto the terminal contacts ot the callec. subscribers line, a releasemagnet for returning said' 'switch under the control ot the callingsubscriber tor selecting an idle one oit said coin nector switches,means tor operating said connector switch to e.\;tend the call to thecalled subscribers line, release means for said connector switch. and aplurality of relays for said connector switch that remain energizedwhile the connector is in use to prevent an operation ot said releasemeans.

6. A telephone system including vsubscribers7 telephone lines dividedinto groups, automatic progressively movable connector switches likewisedivided into groups correspondingy,` to the groups ol subscribers lines,automatic trunking means divided into groups and individual to thesubscribers line groups, subscriber controlled means for actuating saidautomatic trunking means whereby substantially simultaneous connectionsmay be extended from the calling subscribers lines of one group toconnector switches in another or the saine group, and relays tor cach ofsaid connector switches, a plurality ofthe relays of any one connectorswitch being adapted to reliti

